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Tuesday, December 30, 2008

My boss Dr. Alfred McEwen has given me permission to post the presentation on the Io Volcano Observer (IVO) mission concept he gave a few weeks ago at the Io Workshop in Berkeley, California. You can find the presentation here. The presentation covers mission design, mission goals, baseline and optional payloads, and risk assessment.

Mission Design

The current mission design calls for a January 2015 launch (with a window from late 2014 to early 2015). IVO would be launched into a Venus-Earth-Earth gravity assist trajectory, similar to the interplanetary path taken by Galileo between 1989 and 1995. Calibration for IVO's various instruments would be performed during one of the Earth encounters, though McEwen does note that an asteroid encounter during one of the apohelions could be used as a dress rehersal for the Io flybys.

After a six-year cruise, IVO would enter orbit around Jupiter in 2021. Prior to Jupiter orbit insertion, IVO would perform its first flyby of Io. While other information I have found suggested that no science would be acquired during this first encounter, McEwen presentation points out that the reason for performing this encounter is to acquire unique equatorial science since the encounter doesn't actually reduce the delta-V, like the inital Io flyby did for Galileo. IVO would be inserted into an inclined, 200-day-long initial orbit following JOI.

During IVO's orbital tour, planned to last at least 1.5 years, the spacecraft would flyby Io at least six more times, with the goal of having more than ten flybys with the help of an extended mission. With the various sources I have, I am not certain if they plan to have six flybys during the primary mission with at least four more during an extended mission, or if the six-flyby number is only a baseline for mission success. The trajectory design calls for the Io flybys to also be used to "pump down" the spacecraft's apojove, eventually bringing IVO's orbital period down to 30 days. The first few flybys of Io would be further out, with altitudes between 500-1000 km, until estimates of Io's position are refined. Later encounters can then be brought down to altitudes approaching 100 km, supporting magnetometer and mass spectrometer science. Like Galileo, data would mostly be taken during the few days surrounding perijove and would be transmitted to Earth near apojove, though the much greater bandwidth with IVO would support more apojove science, such as imaging of Jupiter and eclipse observations of Io and Europa. Also, thanks to IVO's increased bandwidth, up to 20 Gb of data would be returned after every flyby, much greater than Galileo's entire Ionian dataset. I can't recall, but that maybe more data than Galileo returned during its entire Jovian tour.

For planetary protection purposes (God forbid we contaminate poor Amalthea), the spacecraft would be impacted with Io at the end of its life. However, several end of mission scenarios have been developed, including one that would put IVO into very large orbits, with periods up to one-year in length, in order to monitor Io for up to a decade and to perform a lifespan test for the Advanced Stirling Radioisotope Generator (ASRG), the next-generation power source to be used by IVO. In another scenario, IVO's perijove would be raised to pull it out of the worst of Jupiter's radiation belts, again to extend the spacecraft's life, though there maybe issues with the requirement to dump IVO on Io at the end of the mission.

Mission Goals

Io Volcano Observer, being half a science mission and half a engineering test, has a very focused set of mission goals. As you can see in the slide at right, the primary objective of this study is to see if an Io mission can be accomplished with a Discovery budget, assuming NASA furnishes the ASRG and NEPA.

The baseline mission was designed as simply as possible while still accomplishing a focused set of science goals. From the presentation, these include:

Understanding active Ionian volcanic processes

Understanding the process of tidal heating

Understanding loss of material from Io and following that material to the magnetosphere, plasma torus, and neutral clouds

IVO's planners also want to test out the ASRG for as long as possible, thus the desire to extend the lifespan of IVO as long as possible before crashing it into Io. In additions, measurements of the radiation environment will help planners of future missions to the Jovian system.

There are also secondary goals to study the rest of Jovian system. Most of these observations would be acquired near apojove. These include: monitoring of Jovian clouds systems near the poles (complementing data from Juno), distant observations of the Galilean satellites including Europa's atmosphere, close-up observations of Jupiter's inner moons near perijove, and observations of Jupiter's rings and the Io Plasma Torus. Due to data volume restrictions on the later, shorter orbits, many of these observations would be acquired during the initial, 200-day orbit, when data volume would be more plentiful.

Payload

At the Io workshop, McEwen presented details on the planned baseline payload as well as other instruments that could be used on IVO. With this payload, McEwen and his team hope to accomplish the science goals discussed above.

The baseline payload for IVO includes the following instruments: a narrow-angle camera with an angular resolution similar to Galileo, a thermal mapper similar to THEMIS on Mars Odyssey, an Ion and Neutral Mass Spectrometer, and magnetometers. Other potential instruments outlined by McEwen include a wide-angle camera, a near-IR spectrometer, and an EUV/FUV spectrometer.

The narrow-angle camera, as outlined by McEwen, would provide medium-resolution surface monitoring and high-resolution surface imaging during flybys, while keeping noise to a minimum. Unlike most spacecraft imagers in use, the camera would use a CMOS focal-plane system with both framing and pushbroom modes. The fast readout times for the CMOS system would help keep radiation noise down by reducing the amount of time between the image exposure and its storage in memory. The CMOS detector would be split up so that the bottom half of the detector (1000 lines by 2000 columns), would be used for clear filter, framing-mode imaging, similar to Cassini's ISS. Up to half of the detector would be used for color filter, pushbroom imaging, similar to the Mars Reconnaisance Orbiter's HiRISE camera. This upper section would consist of up to 15 color filter strips of 64 lines each. These strips would use digital Time-delay Integration to produce nearly simultaneous color imaging (necessary for lava temperature measurements), super-resolution, and faint-target imaging. At minimum, McEwen's group would like to include broadband UV, blue-green, red, and near-IR dTDI lines, though other filters could be included, mostly narrowband filters designed for spectroscopy.

IVO's thermal mapper would be designed much like Mars Odyssey's THEMIS instrument. The instrument would include at least three bandpasses between 2 and 20 microns and would have a resolution about 12.5x coarser than the NAC (assuming new detectors are used, compared to THEMIS). With Thermal Mapper, IVO planners hope to map and monitor Io's thermal emission, perform thermal emission spectroscopy, and analyze Io's polar thermal emission and compare it with results from Galileo at low latitudes. For a baseline mission, the expected bandpasses would be at 2, 5, and 20 microns, though more bandpasses maybe possible. Some that interest IVO planners occur between 7 and 9.5 microns, wavelengths diagnostic for silicate mineralogy.

The Ion and Neutral Mass Spectromter (NMS) was covered recently in a blog post, so check that out for details of that instrument. IVO planners seem confident that they can detect most of the expected species in Io's atmosphere (like SO2, SO, O, and NaCl) thanks to its high signal-to-noise ratio and 1-300 amu mass range.

The final pieces of the baseline payload are a pair of fluxgate magnetometers. These very small magnetometers would be attached to 1-meter long brackets bolted to the spacecraft. These magnetometers would be similar in design to those carried on recent ESA planetary missions. Now whether they would actually find a magnetic field at Io...

These instruments would be bolted to the top deck of the spacecraft, below the High-gain antenna. This would force decisions between having a gravity pass and a remote-sensing pass, much like Cassini. Much of the electronics for these instruments would be stored below this top deck, in a radiation-shielded "vault", in hopes to reduce the chances for radiation affecting measurements.

Risks

A major limiting factor for the lifespan of IVO is the high charged particle environment near Io. Even with the high-inclination orbits, IVO planners expect betwen 115 and 230 krads, though the spacecraft electronics may have a much reduced exposure during the primary mission.

Another issue is the current projected price tag. A JPL Team X assessment in November came up with a cost $471 million. I'm not sure if that is for the baseline mission, but at least $21 million will need to be trimmed from the estimated budget to get IVO within the Discovery costcap.

Conclusion

This presentation lays out a pretty compelling case for a cost-effective mission to Io. As of earlier this month, IVO planners were preparing to finish their final report for the DSMCE program and were looking forward to submitting this proposal for the next Discovery Announcement of Opportunity coming (hopefully) sometime around mid-year.

Monday, December 29, 2008

I was alerted to this video by Emily Lakdawalla on her Planetary Society Blog and ilbasso on Unmannedspaceflight.com. It shows the effects of a beam from a proton particle accelerator on a poor, helpless webcam. These effects are analogous to those seen in spacecraft photos due to the impact of cosmic rays and charged particles on spacecraft camera CCDs. During processing these noise hits are removed, though some, like the streaks and snow effect shown in the video, often need to be removed by hand.

An example of one I worked on was a sequence of images of Saturn's moon Epimetheus acquired last year. These images were some of the highest resolution images that will be taken of this moon during the Cassini mission. The images were acquired when Cassini was between the E and G rings, where charged particle radiation was highest and its effect on the images taken can be seen in the raw data. With the help of noise filtering, manually removing stubborn streaks and noise "blobs", and summing multiple images together to improve signal-to-noise, I managed to create a cleaned-up, final product.

Noise hits from charged particle radiation are also a problem with Io images. Io orbits within one of Jupiter's most intense radiation belts: the Io Plasma Torus. Particles from this radiation belt, composed of electrons and heavy ions like sulfur, oxygen, and sodium, can produce noise in images and affect other electrical systems on a spacecraft (like causing safing events, damaging the summation mode of a camera and the grating of a spectrometer).

Monday, December 22, 2008

Next year is the season of eclipses in the outer solar system. Both Jupiter and Saturn will both see the beginning of northern spring next summer. Equinox at both planets also means mutual event season. Astronomers use this time to observe occultations of two moons, when one moon appears to pass in front of another (see this example from Cassini, when Rhea passed in front of Enceladus). Mutual event season is also a season of shadows, when the shadows of the giant planets' moons cause eclipses on other moons or the rings.

At Io, the scientifically most useful type of mutual event have been occultations. By monitoring the brightness of Io as another moon occults it, an astronomer can determine the location of hotspots on the surface by measuring the time when bright IR sources are occulted then later reappear. Robert Howell measured quite a few of these occultations during prior mutual event seasons in 1996-1997 and 2003. See his LPSC abstract from 2003 for an overview. Using these occultations, Howell could not only determine whether or not Loki was active, for example, but also which part of its patera was hot. Recent developments in adaptive optics technology have greatly improved the spatial resolution of ground-based observations, seemingly reducing the need for making such measurements now that they rival them in resolution. However, these adaptive optics observations are only performed at a few of the largest telescopes in the world, like Keck and ESO, which may observe at best a few nights out of the year. Occultation measurments can be acquired by much smaller telescopes equipped with a high-speed, infrared photometer.

The only potential barrier to the events being observed next year is that Saturn will be undergoing a similar ring-plane crossing at about the same time. With a larger orbit, Saturnian equinoxes happen more rarely, every 15 years as opposed to every 6 years for Jupiter. With Cassini in orbit around Saturn making concurrent observations, this ring-plane crossing has even more importance. Therefore, Jupiter's mutual event season may take a lesser priority for astronomers worldwide. [NOTE: After publishing this post, I saw a NASA press release mentioning that Saturn's ring plane crossing will occur as Saturn nears conjunction, when Saturn will be near the sun. So maybe Jupiter's mutual events won't take as much of a backseat since so many of the "good" events occur around opposition, when Jupiter will be opposite the sun in the sky.]

In addition to equinoxes, Io will experience eclipses of the Sun by two other Galilean satellites: Ganymede and Callisto. All but two of the total eclipses seen from Io will be by Ganymede. Ganymede eclipses occur a week, beginning on June 9 and ending on August 5. The early eclipses are best seen in the north polar region, while the later eclipses are best seen over the south polar region.

Here is an overview of the most interesting eclipses:

The eclipse covering the most terrain on Io will be the total solar eclipse by Ganymede on July 15, 2009 at 10:47 UTC. The total solar eclipse will be visible across much of Io's sub-Jupiter hemisphere between 48 North and South latitude, and 232-52 West longitude. The polar regions will experience a partial eclipse. During the eclipse, Ganymede will appear 13' 17.2'' across in the sky (compared to our moon, which appears around 30' across in Earth's sky). The sun will appear 6' 19.9". Therefore, it is unlikely that the sun's corona would be seen during the eclipse except near the beginning and end. At its peak, the eclipse will last 1 minute and 55 seconds long.

The only total solar eclipses by Callisto visible from Io will both occur on June 20, 2009. These eclipses will primarily be visible in the south polar region of Io, on the trailing hemisphere side. The first eclipse occurs at 04:32 UTC, while the second occurs at 09:01 UTC. A third total eclipse would be visible on June 3, however totality starts after a Jovian eclipse has started. June will also see two, multiple Ganymede eclipse days, with two eclipses on June 9 and three on June 16.

Wednesday, December 17, 2008

In this month's issue of the journal Planetary and Space Sciences, there is a review for Ashley Davies's tome Volcanism on Io: A Comparison with Earth. I took a look at the book back in September, giving it a favorable review. In PSS, University of Bern researcher (and INMS instrument co-I on Io Volcano Observer) Nicolas Thomas also gave the book a favorable review. Thomas writes that the book provides a great overview of this increasingly important topic, particularly as NASA seems to be getting serious about a return to Io. He notes some minor issues with the book, such as its scant coverage of theory behind tidal heating and gas plume modelling. The latter was a problem I had, particularly when you compare it to the coverage of the modelling of Ionian lava flows.

Besides being a straight review, Thomas provides an often amusing look at the problems facing a future Io mission and the reasons why Iophiles should take heart that an Io mission may not be impossible. Besides the usual concerns about radiation and the need for RTGs for power (I was reminded last week that you need RTGs to return data at a high bitrate from Jupiter -- read pictures -- so don't look for me to post that solar-panelled Io mission anytime soon), Thomas notes the programmatic problems with the lack of water and the potential for life on Io. These of course clash with NASA's recent obsession with following the water and astrobiology. However, Thomas tries to sooth these concerns by noting NASA's need to test their next-generation radioisotope power sources (ASRGs), which led to the IVO concept study, the innovative high-inclination orbits to be tested by Juno that would reduce a spacecraft's radiation exposure, and the desire to test rad-hard technology for a future Europa Orbiter.

Kane, in his blog post, took a look at a presentation given at this year's Io Workshop, held at the UC Berkeley last week, given by Alfred McEwen. Among the new details on the proposal include a refinement on the mission profile, with a proposed launch now seen in January 2015 with a Venus-Earth-Earth trajectory to Jupiter. Jupiter Orbit Insertion, including the first Io flyby, would occur in 2021. IVO would be injected into a high-inclination orbit around Jupiter in order to limit the spacecraft's exposure to the planet's radiation belts, thus extending the lifespan of the spacecraft. As previously reported, the initial orbit would be an eccentric, 200-day orbit, which would be reduced in length using later Io flybys. The baseline mission calls for six Io flybys over a 18-month long primary mission, with more flybys in a possible extended mission.

The current projected mission cost is $471 million, slightly above the current Discovery mission cost cap of $450 million and also assumes that the ASRG power sources would be provided by NASA.

Many of the details of the instruments planned for IVO remain similar to those reported here before. Two magnetometers appears to have replaced the radiation detector in the baseline payload.

Monday, December 15, 2008

Okay, it has been a while since I have discussed the Io Volcano Observer (IVO). This mission concept was developed in response to the Discovery and Scout Mission Capability Extension (DSMCE, pronounced DOS-MICE). The DSMCE program was started by NASA to examine the viability of Discovery-class mission powered by next-generation radioisotope power generators provided to the PIs at no cost to the mission. The IVO study is headed by Alfred McEwen at the University of Arizona with scientists and engineers at Ball Aerospace, USGS-Flagstaff, JPL, and the University of Bern in Switzerland.

Well, obviously, despite the fact that the initial study is finished, very little has shown up on the web. There is a good reason for that. There is a very good chance that McEwen et al. will submit a proposal for the mission with the Discovery Announcement of Opportunity is released next year (April 2009?). Despite this, I have found a new online source for information on the mission, particularly on the Ion and Neutral Gas Mass Spectrometer (INMS) from a presentation given by the Peter Wurz of the University of Bern in October.

The presentation's fifth slide provides an overview of the IVO mission, mostly with details that were previously known. Three instruments are planned for IVO's payload: a narrow-angle camera, a thermal infrared imager, and an ion and neutral mass spectrometer. A Radiation Detector and Ultraviolet Spectometer are not mentioned, like in Dr. McEwen's presentation in May. The baseline mission plan remains much the same as was outlined by Dr. McEwen: a launch planned for 2013 (with a backup in 2014), Jupiter orbit insertion in 2020 with the first Io flyby in June 2020 (a year later than the baseline mission presented in May), and a science phase that runs 16 months to October 2021. Considering that the initial Jovian orbit following the first Io flyby is expected to run on the order of 200 days, the other nine flybys are planned between December 2020 and October 2021 occurring on the order of about once a month.

Dr. McEwen's presentation at LPSC went into a bit of detail of the Narrow-angle camera and the thermal imager, but he ran out of time before he could get to the INMS. Therefore, the presentation by Wurz is complementary to McEwen's. IVO's INMS is a time-of-flight mass spectrometer with some design heritage with the ROSINA instrument on Rosetta. P-BACE, a spectrometer similar to the one planned for IVO, was developed at Bern and was aboard MEAP, a stratospheric balloon mission that recorded measurements of the circumpolar wind patterns between Sweden and Canada. Based on the measurements acquired by P-BACE, Wurz and Thomas expect to be able to measure most of the atmospheric species expected at Io, such as sulfur dioxide, sulfur, hydrogen sulfide, sodium, potassium, and oxygen.

The scientific goals for IVO's mass spectrometer include: measurements of Io's atmospheric scale height and major components; a search for differences in these measurements as a result of temporal changes, geography, or day-night cycles; measurement of atmospheric loss mechanisms and rates (due to sputtering for example); and measurements from within a volcanic plume.

Overall, the INMS looks like an interesting addition to the mission. The instrument could also take on increased importance as a similar instrument may not make it on the Europa Orbiter since the instrument would push the cost of the EO above that project's budgetary "sweet spot." So even if Europa Orbiter is selected as the next Outer Planets flagship mission, IVO might still get proposed because of unique measurments a mass spectrometer could make. IVO could also provide a useful stopgap between New Horizons and EO (planned to arrive in the late 2020s).

(Before you ask, the graphic at the top is an old, 1990s-era graphic of IVO, so just ignore the solar panels ;)

Van Kane has a great post on his blog, Future Planetary Exploration, on the potential for future New Frontiers-class (or Discovery-class) missions to Io. This is the first in a series of posts on mission concepts and the likelihood of an Io mission. Definitely worth checking out.

I will try to post more on the solar paneled Io mission concept later today.

Tuesday, November 25, 2008

The New Frontiers-3 Draft AO is now online. The Announcement of Opportunity states that following classes of mission proposals will be accepted: Aitken Basin Sample Return, Venus in Situ Explorer, Comet Surface Sample Return, Network Science, Trojan/Centaur Reconnaissance, Asteroid Rover/Sample Return, Io Observer, and Ganymede Observer. The cost cap has been set to $650 million in FY09 dollars and will be not be permited to use radioisotope power sources. This would make a potential Io Observer difficult, but NOT impossible due to the radiation environment at Io (I will get to why it isn't impossible in a later post). Despite the National Research Council's recommendation, the AO was not opened up to "all missions except to Earth and the Sun that fit within the budget and power source constraints," as Jim Green promised back in March.

Van Kane has a great post comparing the virtues of the Saturn/Titan and Jupiter/Europa missions now vying for the flagship mission spot. I think Van hits the nail on the head here. I will post a similar recommendation post soon.

Monday, November 10, 2008

The Volcanism on Io Wikipedia is now featured on the main page of the popular encylopedic website, giving millions of people a chance to learn more about this fascinating word. Thanks to all who helped in bring that article to this point!

Phoenix has finally kicked the bucket. A sad day, but not unexpected given the changing seasons in the Martian arctic. Congratulations go out to the Phoenix lander team for producing such a successful mission.

I have added the Follower applet on the sidebar at right. So feel free to show your support for my blog.

The presentations for last week's OPAG Fall Meeting are now online. These include several presentations covering the two Outer Planet Flagship mission proposals, the Europa/Jupiter System Mission (EJSM) and the Titan/Saturn System Mission (TSSM), as well as other programmatic presentations.

The final reports for the two proposal teams were due last Monday so last week's OPAG meeting were the first opportunity to present the finalized proposals. These include a more detailed sample mission profile, payload, and science goals. EJSM would include two mission components: the Jupiter Europa Orbiter (JEO) and the Jupiter Ganymede Orbiter (JGO). According to the baseline mission plan, the two components would launch separately in February and March 2020. JEO would arrive at Jupiter in December 2025 while JGO would arrive in February 2026. JEO would then conduct an orbital tour of the Jupiter system over a period of 31 months, before entering orbit around Europa in July 2028. During the Jupiter tour phase, JEO would perform more than two dozen flybys of the Galilean satellites. JGO would conduct a more focused tour of the outer two Galileans before going into orbit around Ganymede in late February 2028. There are hints in the presentation that JGO might attempt to encounter one of the outer irregular satellites during its mission.

The NASA-supplied component, JEO, would encounter Io four times during its mission. The first encounter would occur just before Jupiter Orbit Insertion (JOI), and like the flyby before Galileo's JOI, the Europa Orbiter would not acquire science during Io-0. During the other three encounters, performed in the second half of 2026, 25% of Io's surface would be imaged at better than 200 meters/pixel. The last of the three encounters would occur at an altitude of 75 kilometers, enabling direct plume sampling, though the current sample profile would not allow for sampling of any known plume except for maybe the outer reaches of the Culann plume. It should be noted though that the tours shown are just examples that are subject to change. For example, the Cassini prime mission tour wasn't approved until a few years before it arrived at Saturn. The presentation goes on to mention that the radar instrument on JEO would be active for the flybys allowing for sub-surface sounding and altimetry. These could be useful in constraining tidal heating models and near-surface lithospheric structure. Another interesting slide in the EJSM presentation is the data return plan. The EJSM team plans to return 3 Gb per day from Jupiter during the tour, providing for hundreds of narrow angle camera images per day along with context images from other imagers. This could provide very decent monitoring of Jupiter and Io processes. Finally, the JEO team plans to image Io once or twice a week while in Europa orbit for monitoring purposes.

The payload for EJSM seems pretty capable. In addition to three camera systems (narrow-, wide-, and medium-angle cameras), the payload includes: a laser altimeter, an ice-penetrating radar, a Visible-IR spectrometer, an UV spectrometer, and Ion and Neutral Ion Spectrometer, a thermal instrument, a magnetometer, and a plasma and particle instrument. The communications antenna on JEO can also be used for radio science experiments. The specific instruments will be selected via an annoucement of opportunity. The JGO would carry a similar payload.

EJSM faces competition with TSSM for the Outer Planet Flagship Mission. TSSM would provide a NASA Titan orbiter, an ESA balloon, and an ESA lander planned for central Kraken Mare.

There is some disagreement between the presentations about when the downselection will occur. The EJSM presentations suggests that down-selection occurs in January 2009 with a confirmation of this selection by the ESA Science Programme Committee on February 4 (the ESA component would be formally approved at the end of 2012, where the component would have to compete with Xeus and LISA). A presentation by Curt Niebur still uses mid-February 2009 as the downselection date.

Tuesday, November 4, 2008

I am deeply saddened right now. Our country has gone in a very wrong direction tonight and I just don't know what to say. Shocked. Saddened. Horrified. I recognize the choice of the majority in this country, but still... wow. I hope my worst fears are not realized. I hope in four years we will be better off. I am proud to some extent of the historic choice the country has made, but I feel that this particular candidate was not the right one for this time in our history.

I believe this country can be a great one. However, I think that can only be done by not looking to the solutions of the past, which I felt Obama represented, but by look for the solutions of the future. I believe that the presidency is not a popularity contest. I believe the presidency requires the culmination of a lifetime of political and lifetime experience.

A few things I will be doing is reading up on the 1917 Russian Revolution so I will know what to do. Probably go back to burying myself in work I guess.

I guess what that means is no more politics here. Sorry, I just needed to get a few things off my chest. This is just such a tragic day.

Monday, November 3, 2008

The final reports for the two Outer Planet Flagship teams, the Europa/Jupiter System Mission (EJSM) and the Titan/Saturn System Mission (TSSM), were due today. I have no idea when these reports will be available online, but both teams will be making the first of their final pitches later this week at the Outer Planet Assessment Group meeting in Tempe, Arizona. Presentations from that meeting should be available much sooner than the final reports, giving us a look at what the final missions will look like.

Wednesday, October 29, 2008

To all those who know me: if current national polls hold up, I will be in an incredibly foul mood come next Wednesday. Please don't take it personally. I will get over it eventually. I will try not to bring it here on this blog but be warned that I may post something about "gullible people" or some such next week. Hmm, from that last sentence, I may already be in a foul mood...

Meet Reiden Patera. On the surface, it is an ordinary volcanic pit on Io. But in reality, it is anything but ordinary. Every few years, this particular volcano becomes just another part... of the Twilight Zone.

Okay, I am not Rod Sterling. However, today I thought I would write a little post on this curious volcano. Actually, it is quite ordinary. Our best resolution images are at only 1.5 km/pixel. It has never been the site of an outburst. However this volcano in the shadow of Pillan has gone through an interesting cycle of activity since the feature was first observed by Voyager 1 in 1979.

Reiden Patera is a 73-km wide volcanic depression located on Io's trailing hemisphere a couple hundred kilometers to the southwest of Pillan Patera. Reiden's proximity to Pillan causes occasional confusion between the two features when trying to identify the source of thermal emission in eclipse and near-infrared images of this region of Io. Reiden generally has a dark green floor with dark spots scattered around the margin of the patera. Surrounding the patera, there is normally a bright annulus, which is then surrounded by a dark annulus. The closest analog seen at high resolution by Galileo would be Camaxtli Patera, a similar-sized volcano on Io's anti-Jupiter hemisphere. Like Reiden, Camaxtli has a floor with a patchwork of bright deposits and dark lava flows, and has concentric bright and dark halos surrounding the depression. Reiden, like Camaxtli, has a roughly polygonal outline, with several straight margins, suggestive of structural control, by pre-existing tectonic faults, of the patera margin. A possible landslide deposit can be seen along Reiden's northern margin.

As you can see in the above montage, the appearance of Reiden changed during the course of the Galileo mission. During the first few orbits, several dark spots were seen along the margin, some appearing over time. This suggested on-going volcanic activity centered on the patera margin, and this is substantiated in the thermal data acquired by NIMS and SSI. The camera onboard Galileo, SSI, detected a hotspot at Reiden during the mission's first orbit in late June 1996 (G1). NIMS, the near-infrared spectrometer on Galileo, may have detected a hotspot at Reiden during the second and third orbits (early-September and early-November 1996, respectively), though Lopes et al. 1997 attributes the observed thermal emission to Pillan instead. Changes observed in images acquired in February 1997 (E6) suggests that Reiden was active until shortly after the November 1996, but SSI did show that Reiden had decreased in activity by E6 (in fact, Reiden was not visible in SSI eclipse observations like it was in G1). The lack of changes in images acquired in April 1997 (G7) provides further evidence that the eruption at Reiden had ended. By the next orbit, the outburst eruption at nearby Pillan had begun.

Over the next few years, Reiden remained an inactive volcano, and the dark lava flows seen along its margins began to turn from black to dark green. In images acquired in September 1997 (C10), even the dark halo surrounding Reiden was gone, but the inner, bright halo remained. How much topography and the nearby Pillan eruption played in this change isn't clear, but it appears that Reiden's bright halo maybe located on a low, topographic rise that surrounds Reiden as it was not covered by Pillan's pyroclastic deposits and the topographic rise acted as an impedment to the pyroclastic flow. This provides further evidence that Io's dark silicate deposits, associated with some volcanoes like Pillan, Tvashtar, Pele, and Babbar, are deposited in a process akin to terrestrial basal surges compared to the umbrella-like gas plumes Io is so famous for. As Pillan's dark deposit faded in 1998 and 1999, the dark halo seen when Reiden was active remained absent.

Reiden reactivated by late 2000 as it was seen as a hotspot by Cassini ISS during that spacecraft's distant flyby on December 30, 2000. Galileo during this time observed a darkening at Reiden, further suggesting that activity had resumed. In addition, Galileo observed fresh reddish deposits to the east and northwest of Reiden, perhaps from this new eruption. During a flyby in October 2001 (I32), Reiden was seen at higher resolution. This observation revealed fresh dark material (compared to comparable data acquired in October 1999) along most of its margin, except to the north (where there is a landslide). Reiden may have reactivated as early as October 1999 (I24), when two dark spots were observed along the margin of the patera, near its southwestern margin and along the southern part of the landslide deposit.

Reiden was also seen as active by New Horizons in LORRI imager data and was seen as a dark feature with a bright halo. During the Voyager flybys, it appeared similar to its appearance during the first few orbits of the Galileo mission, though with a dark spot along its northeastern margin, suggesting that Reiden was active during the Voyager mission.

Reiden, though named after the Japanese god of thunder (or was it the Mortal Kombat character...), has long been in the shadow of more famous volcanoes like Pillan and Pele, volcanoes that occasional affect the appearance of Reiden and its surrounding terrain. However, the history of activity at Reiden is an interesting one, where several distinct eruption cycles have been observed by multiple spacecraft. All of Reiden's activity has been confined to small effusive eruptions along the depression's margins. This would suggest that perhaps Reiden is a large lava lake, but there is no evidence of a massive crustal recycling event like those seen at Loki, a more classic example of a lava lake on Io. It is possible that magma uses the faults that bound the depression as conduits to reach the surface, explaining why flows are confined to the margins of the patera. However, a passive lava lake would explain the small eruption along the southern margin of the landslide deposit seen during C3 and I24, as the margin of the landslide would likely not be structurally controlled. It is also possible that this northern bright area is not a landslide, but a cool "island", similar to those seen at Loki and Tupan, two volcanoes thought to be lava lakes.

Hope you all enjoyed this look at Reiden Patera. I hope to post similar articles about other "forgotten" volcanoes here in the future.

Tuesday, October 28, 2008

Abstracts for the AGU Fall Meeting are now online. This now gives us a chance to look at some of the Io-related talks and posters to be presented at the December meeting:

Dave Williams will give a talk on December 19 titled, "Volcanism on Io: Insights from Global Geologic Mapping." Williams will describe work his group performed on a new global geologic map of Io that uses a new USGS global mosaic. Geologic maps for other planetary bodies define different morphologic features on the surface, as opposed to terrestrial geologic maps which are ususally based on the mapping of different rock layers. One interesting conclusion they make is that bright lava flows cover more of the surface than dark flows, with some bright flows not being adjacent to dark flows, suggestive of primary sulfur volcanism at some locations. I should point out that many dark flows turn bright over time (like Thor).

Windy Jaeger will present a poster on December 18 titled, "Lithospheric Structure and Patera Formation on Io: Implications for Future Observations." As the title suggests, the poster will present how the structure of the lithosphere may influence the formation of volcanic depressions on Io. Jaeger's lithosphere model suggests that the upper few kilometers of the lithosphere consists of interbedded layers of SO2 and cooled silicate lava flows. Below this, silicates dominate with fewer volatiles. When magma rises to the surface, it stalls when it reaches the interface between these two sections, forming sills. These sills then sublimate the SO2 above it, the new void forming a depression, a patera. Jaeger suggests that this model could be tested by future spacecraft by acquiring high-resolution images of patera and mountain flanks, as well as medium-resolution stereo observations acquired over a period of at least a year.

In "Lava Fountains on Io: Implications for the Interior and Future Observations," Laszlo Keszthelyi looks at the same problem from a different approach. He suggests that imaging lava fountains would be useful for determining Io's lava composition. To accomplish this, data would need to be acquired over multiple filters over a very short period of time, likely less than 0.1 seconds. The camera system planned for the Io Volcanic Observer would image Io in four filters simultaneously for this very reason.

Monday, October 20, 2008

Now that DPS is finished, we have hit a bit of a lull in the news cycle, but here are a few quick updates:

The Volcanism on Io article on Wikipedia has now reached Featured Article status, applied to articles on the site that are considered its best work. This now makes two Io-related Featured Articles, as opposed to just one for Europa...

October 20 has almost come and gone, and the abstracts for the AGU Fall Meeting are not online yet. I will post here when they are.

Friday, October 17, 2008

I have been slowly working these last few weeks on this quick little Science Fiction short story that takes place on Io and Europa, titled "Invincible." I have posted the first draft online and I want to let you all take a look at it. I should point out that it does have some strong language, so if you don't think you would be comfortable with that, well, I thought I would give you heads up.

As to what to expect, I was going for a kinda "Munich" in space. Okay, maybe that's a bit over-simplistic, and it certainly doesn't cover all the kinds of issues that Munich did, but that's the best I can come up with at 2am in the morning.

Wednesday, October 15, 2008

The Galilean Satellites session at the DPS meeting was held this morning in Ithaca, New York. The talks were also online as a webcast, allowing me to view (and all of you) to view the talks despite not being at the conference. The talks mostly focused on the icy satellites of Jupiter, particularly Europa and Ganymede, but two talks covered Io specifically. The first was given by Julie Rathbun (with co-author John Spencer) and was titled, "Loki, Io: Fitting a lava lake model to Eclipse Observations" (link takes you the abstract). The second was given by Nick Schneider (with coauthors C. Grava and C. Barbieri) and was titled, "Unusual Velocity Structures of Neutral Sodium Near Io's Wake."

Rathbun presented ground-based data of Io at multiple wavelengths in the near-infrared portion of the spectrum. This was done to see if the lava lake crust floundering model for Loki's eruption behavior was supported using multi-wavelength observations.

Ground-based observers have been monitoring activity at Loki Patera, the largest volcanic depression on Io, since 1988. This observation campaign has revealed that Loki goes through a cycle of activity, with periods of high-thermal emission (also called brightenings) and low emission. The Rathbun model suggests that this cycle is related to the style of activity at Loki. She (and her co-authors) propose that Loki Patera is a large lava lake, a depression filled with molten lava and covered by a thin crust of porous, solidified lava. Over time, this crust thickens to the point where the crust starts to collapse. This collapse occurs as a wave, moving from the southwest margin of the patera then counter-clockwise around the interior "island" to the northwest margin. A new thin crust forms behind this collapse wave, and is allowed to thicken until it is no longer bouyant over the molten lava below.

To test to see if this model is supported at multiple wavelengths, Rathbun examined disk-resolved Io images taken at NASA's Infrared Telescope Facility (IRTF) at 2.26 μm and 4.78 μm (similar to the image at right), to go along with the 3.5 μm observations used to develop their lava lake model. Using the model, which takes into account the average duration of a brightening event and the average peak 3.5 μm brightness during these events, they can predict the brightness of Loki at the other two wavelengths and the amount of power output in Gigawatts per micron per steradian. For the 3.5 μm observations, Rathbun and Spencer used occultation light curves, disk-integrated measurements of Io's brightness as it either leaves or enters Jupiter's shadow. Knowing the position of Io and the timing of these measurements, the authors can extract a position for any thermal emission source seen in the lightcurves.

For the disk-resolved images at the other two wavelengths, Rathbun and Spencer had to subtract the contribution from the other volcanoes on the sub-Jovian hemisphere to obtain an estimate for the brightness of Loki. Rathbun accomplished this by comparing global brightness measurements derived from the IRTF images between periods when Loki was active and when it was inactive. By subtracting the average global brightness between those two periods, she could get an estimate of Loki's average brightness during a brightening at 2.26 μm and 4.78 μm. The estimates had pretty large error bars, but the estimates seem to fit the predicted values from her lava lake model. This technique was also performed with IRTF observations at 3.5 μm, and they fit the occultation light curve measurements.

Rathbun and Spencer plan to compare the 2.26 μm estimates to a couple of lightcurve measurements at 2.2 μm accomplished during the Galileo mission. They also plan to look at the individual observations from the Galileo era when they had great temporal resolution.

The other talk, by Nick Schnieder, covered "Unusual Velocity Structures near Io's Wake." Io's atmosphere (and ultimately its volcanoes) supplies material for various structures in Jupiter's magnetosphere. Schneider used a spectrograph at the Telescopio Nationale Galileo in the Canary Islands to observe the various escape features for sodium in the banana-shaped neutral cloud that surrounds Io as Io went into and out of Jupiter's shadow. These include streams of fast moving sodium atoms from the neutral cloud and jets of sodium from Io's ionosphere. Schneider's observations revealed an additional escape mechanism. In this case, sodium jets away from Io toward Jupiter at only 15 km/sec. This suggests the sodium originates on the Jupiter-facing hemisphere and is perhaps limited to the leading hemisphere. How these jets are generated has not been determined. However, this new sodium features may provide a new way to study Io's volcanism, atmosphere, and plasma environment from Earth.

That finishes up the Io talks for DPS. Hopefully, AGU and next LPSC will provide more geology ;)

Tuesday, October 14, 2008

NASA Night at DPS just ended a few minutes ago, and I took the opportunity to view the presentations online. In a bit, it should also be archived for everyone to view here. NASA Night is an opportunity from program heads at NASA HQ in Washington to speak to the Planetary Science community about what NASA HQ is doing with respect to the Planetary Science Division at NASA and for them to get input from the community. These events can often be contentious as changed made by NASA HQ with how things are done and what missions and announcements of opportunity are coming up can effect people's funding and lively hood.

There were two presentations given at NASA Night. The first was given by the director of NASA's Planetary Science Division (PSD), Jim Green, and the second was given by the director of SARA (the grant program at NASA), Max Bernstein. There was a question and answer session following each talk.

Jim Green's talk provided the most meat at NASA Night. He discussed the problems the Mars Science Laboratory has been having lately, the upcoming New Frontiers and Discovery Announcements of Opportunity (AO), the next Decadal Survey, the Outer Planets Flagship Mission, and the new travel and conference funding for NASA employees. Obviously he covered quite a bit of territory.

As is known by now, the Mars Science Laboratory recently incurred yet another cost overrun, more than the overguide threshold requied by NASA. This resulted in a review with the adminstrator. From this meeting last week, the adminstrator agreed to keep MSL on the current launch schedule for 2009. However, funding issues remain. The PSD will perform a review of the extent of the overruns, as the JPL estimates appear to lack credibility. Once this is done, the PSD will determine how to cover the costs. Green assured the audience that he will use the Planetary Science Subcommittee's recommendations to only get the funds from missions outside the Mars Program (like Juno) as a last resort, with funding mostly coming out of JPL and the Mars Program (possibly affecting MAVEN). The PSD will then worth with the White House Budget Office and the Congress to finalize a resolution, though with MSL now 30% (or more) over the initial budget estimate, Congress could decide to cancel MSL. At the moment, there are no plans to descope instruments on MSL.

Green next discussed the next Decadal Survey. Decadal Surveys act as a guide for NASA when selecting missions and instruments over the next 10 years. The last Decadal Survey in 2001 promoted Pluto/Kuiper Belt flyby and Jupiter missions as the top priorities for the New Frontiers program, which resulted in the selection of New Horizons and Juno. The last survey also excluded the Mars program from the priority list, since at the time (and still to this day) the Mars program is separate from missions to the rest of the solar system. The next Decadal Survey, scheduled for 2011, will include Martian and Lunar missions. Extrasolar planets will be covered by the Astrophysics Division.

Green next discussed the Discovery and New Frontiers programs. Green briefly covered the DSMCE program (pronounced DOS-MICE). This was a mission concept study program to see what kinds of Discovery-class missions could be performed if the proposers were given two free Stirling Radioisotope engines for energy, rather than solar panels, which have been used for all previous Discovery-class missions. One of the concepts they are looking at is the Io Volcano Observer, a study led by my advisor, Alfred McEwen. Reports from these studies are due in December. The next Discovery AO is planned for 6 months after the New Frontiers AO. Green said that the decision to use government-furnished Sterling engines for this next AO has not been made yet. The next New Frontiers AO is currently being developed. The draft AO will be released soon, and will be available for public comment for three months before the final AO is posted.

Green then briefly covered the Outer Planets Flagship Mission selection. Nothing new to report since the PSS meeting a couple of weeks ago. Green did confirm that the change in the planned launch window, from 2016-2017 to 2018-2022, was done so that the NASA-provided mission components would launch closer in time to the ESA-provided components.

Finally, Green reported that NASA is severely restricting funding for NASA employees to go to conferences as well as sponsorship of conferences. This restriction includes attendance at DPS, LPSC, and AGU. This would limit the number of civil servant employees at these conferences, such as those from JPL and Ames. Jonathan Lunine, during the Q&A session, brought up the argument that this restriction, which maybe temporary, would limit grad students exposure to federal civil servants, which could make employment at NASA facilities less attractive. In additional, the restriction could cause a drop in membership to professional organizations like AGU and AAS as NASA employees would no longer benefit from the reduction in attendance fees at conferences.

Despite still being in Tucson, for the last few days I have been remotely attending the DPS meeting in Ithaca, New York. The DPS meeting (otherwise known as the Meeting of the Division of Planetary Science of the American Astronomical Society... *phew*) is one of the big three American planetary science meetings, which also includes LPSC (generally in March), the AGU Spring Meeting (generally in May), and the AGU Fall Meeting (generally in December). I attended the DPS meeting last year, and even gave a talk on the Cassini camera's observations of Titan's trailing hemisphere.

So this year, I am watching the DPS meeting online via Cornell University's Live Webcasting system. No Io-related results in the talks presented so far, but there were quite a few sessions I was interested in. First and foremost for me were the Titan sessions. In fact, it seems like Titan has replaced Mars in importance at DPS with three Titan oral sessions versus just one Mars surface session.

Perhaps the talks that had most relevence to Io in these Titan sessions were the "Subsurface" talks given yesterday morning. Many of these talks related to surface processes generated by internal activity, such as topography, mountains, and cryovolcanism. The cryovolcanism talks, given by Rosaly Lopes, Bob Nelson, and Ashley Davies, often sounded like Io talks from a few years ago. Lopes discussed RADAR results at a feature known as Hotei Arcus, seen above in ISS data from July's T45 flyby. The RADAR team inteprets some of the features in the region as cryolava flows, composed of water and ammonia. The flows appear to be part of a compound flow field, similar to Amirani and Prometheus on Io. The main body of the flow field appears bright in RADAR, indicating a rough surface. On top of this flow field are several large flow lobes that are darker, or smoother, than the rest of the flow field.

Bob Nelson gave a talk on the photometry of Hotei Arcus and a region in western Xanadu. These two regions correspond to areas where RADAR has seen evidence for compound flow fields. Based on a comparison of several observations acquired by VIMS, Nelson suggests that brightness changes have been observed at these regions, possibly due to fumerolic activity at these sites. With the addition of the RADAR results, Nelson's finding are becoming a lot more convincing. Finally, Ashley Davies presenting a cooling model for cryolava flows on the surface of Titan, similar to cooling models he presented for Io in recent years.

The Galilean Satellites session takes place Wednesday morning starting at 8:30 am EDT (5:30 am Tucson time). You can catch it live or archived following the talk by following this link. The only Io surface-related talk to be given tomorrow is by Julie Rathbun. She will talk about ground-based observations of Loki at multiple wavelengths. I will present a summary on the blog tomorrow afternoon. Also, tonight, the NASA Night session will be presented online at 7:30 pm EDT (4:30 pm Tucson time). These are always pretty interesting. I am not sure if the Outer Planets flagship mission will be discussed, but you can presume the recent headaches over the Mars Science Laboratory will.

Thursday, October 9, 2008

The AGU Fall Meeting Science Program page is now stating that AGU abstracts will be posted online, along with the schedule of session, on October 20. I will post more about the few Io abstracts available then.

The 2008 AGU Fall Meeting takes place December 15-19 in San Francisco, CA.

I want to thank Bruce Moomaw and Van Kane for alerting me to the release of the presentations from last week's Planetary Sciences Subcommittee meeting. This subcommittee meets a few times a year to discuss NASA programs and projects related to unmanned exploration of our solar system. For the most part, this subcommittee is presented with presentations from the individual sub-subcommittees, like OPAG (Outer Planet Assessment Group), as well as presentations on R&A and future missions.

The main story from this meeting was the cost overruns by the Mars Science Laboratory, a next-gen rover currently scheduled for launch late next year. The problems with MSL may cause a launch delay to the next Mars launch opportunity in 2011, but that would tack on more than $300 million to the projects already ballooning price tag. An additional option would be to launch the rover into a solar parking orbit in 2010, before getting to Mars in 2012, but that would still tack on around $300 million to MSL's cost. A decision on MSL's future could come as soon as tomorrow, after a meeting with NASA's administrator. MSL's cost overruns have become so great that they are seriously affecting NASA's other near-term missions, such as Juno (a Jupiter New Frontiers-class mission), GRAIL (a lunar Discovery-class mission), MAVEN, and LADEE. Very quickly, MSL is becoming the beast that ate the Mars program. Mars '16 will probably get kicked, for example, and the sample return mission, will likely remain 15-20 years in the future.

To happier pastures, the Outer Planets Flagship Mission studies both continue to crystallize. Curt Niebur gave a presentation on the current state of that program. They are still looking at a November 3 deadline to turn in their final reports to NASA HQ, with additional site reviews in December and down selection still set for mid-February 2009. The report makes clear that both NASA and ESA will get their heads together to pick a single mission, possibly eliminating the possibility that NASA could decide to launch the Europa Orbiter, for example, and ESA will launch the Titan boat and balloon. From Niebur's presentation, it would appear we can expect not one, but three reports from each team: one describing the NASA contribution in detail, another describing the ESA contribution in detail, and an overall report descibing the missions and how they will link together.

Niebur's presentation also describes how the review process will proceed. NASA and ESA review teams will go over their agency's contributions (for NASA that would be the Jupiter Europa Orbiter and the Titan Orbiter). In February 2009, management from both agencies will come together to discuss their reviews and decided a single project.

Niebur also presented an overview of the Jupiter Europa Orbiter mission. The mission still includes 3-5 Io flybys, likely in a single, "Io phase" of the mission's 24-33 month Jupiter orbital tour phase. Launch is set for 2018-2022. 12 instruments are planned for the "sweet spot" mission.

Tuesday, October 7, 2008

The 2008 Division of Planetary Sciences Meeting will be starting on Saturday and running through next Wednesday on the campus of Cornell University in Ithaca, New York. There is a Galilean Satellites oral session on Wednesday morning and a companion poster session on Monday afternoon. I mentioned a couple of the talks and posters a couple of weeks ago.

I will not be attending the conference, but you and I will still be able to see the oral sessions. Cornell University will be broadcasting all the oral sessions live on the net! So hopefully, I can still provide coverage of the talks here next week. Now if only more conferences did this I really hope this goes well for the DPS so they will do this again next year.

Yesterday was a significant day in astronomy. Yesterday evening, Tucson time, an asteroid 5 meters across streaked across the sky of Chad, Egypt, and Sudan. This kind of event happens routinely, an object 5 meters across encounters our planet about once every few months. What made this rock, 2008 TC3, significant was that for the first time, ever, an asteroid was discovered on a collision course with Earth. We observed it as it approached our planet, and according to some early reports on Spaceweather.com, observed it streak across our sky. No longer is the term "meteoroid" just the name we give to what a meteorite WAS before it hit our planet, we have actually studied a meteoroid in space, before impact.

On the Bad Astronomy blog, a commenter asked, "What is the distinction between a meteoroid and an asteroid?" The answer is that there is none. An asteroid is just a small, rocky body that orbits the sun. A meteoroid is just the term for a meteorite's state before it impacts earth, there is no size distinction. In other words, for the first time, we have observed a meteoroid.

Very cool stuff. Wished it streaked through our sky here in Tucson, but I made do with watching it on simulated on Celestia. Hopefully, some folks in southern Egypt caught it on tape :)

Monday, October 6, 2008

I was working on creating images for Wikipedia for various volcano article that I thought needed working on. Anyways, I ended up making what I think is one of the best color images of Pillan Patera from after its eruption. This color image combines high-resolution clear filter data from I24 (the 24ISSTEREO01 observation) and lower resolution color data acquired nine hours later (the 24ISGLOCOL01 observation). This combines to make a color images of Pillan Patera at ~1.45 km/pixel, but keep in mind that Pillan Patera was near the limb during the high-resolution observation. This image helps make clear some of the relationships between Pillan's lava flows, produced during an eruption in the summer of 1997, and diffuse deposits nearby.

Click on the image at left to see a higher resolution version. The image is in simple cylindrical projection with a resolution of 1.45 km/pixel.

Sunday, October 5, 2008

While the abstracts for the AGU Fall Meeting are not online yet, a list of submitted abstracts is available. There will be an Io Workshop shortly before AGU nearby. Here are the Io-related talks and posters planned for December's meeting:

Saturday, October 4, 2008

The Volcanism on Io article on Wikipedia has gone through quite a few updates since my post on Tuesday, approaching the quality of a Featured Article, IMHO. I should point out that this article covers the physical process on the surface of Io, not the book that I reviewed here last week. The main Io article on the site was made a featured article last year, so this would make the second Io-related featured article on Wikipedia. This week, I also started a few stub articles on Amirani, Prometheus, and Surt. I might take another look at those tomorrow.

Again, don't forget that Wikipedia is the encyclopedia that anyone can edit, so feel free to go through those articles and improve them, even if it is just my grammar ;-)

While Wikipedia is often not the best source of information, or even a good source, it is still the number one search return when people look for almost anything on Google. So more often than not, it is often the first place people will look for information. Why not make sure that the information it has is accurate, thorough, and useful?

Adaptive optics observations of Jupiter, acquired from Chile's European South Observatory, were released on Thursday. These images show Jupiter as it appears in the near-infrared near 2 microns, beyond the light that humans can see. So clearly, these are false color images that were released. But the images still are very cool, showing how the recent reshaping of Jupiter's cloud belts have affected its haze layers higher up in the atmosphere. For example, the brightest part of the haze layer over the equatorial belt has switched from the northern to the southern hemisphere. The observations resulted from a new system that allows the adaptive optics system to use moving reference targets for a longer period of time, allowing astronomers to use the AO system over a larger field of view.

Speaking of ground-based observations of the Jupiter system, amateur astronomer Paul Haese has set up an online gallery showing the observations he has acquired of Jupiter during the last three years. These images have high enough resolution to pick up some of the larger scale albedo markings on Io, like the difference in brightness and color between the polar and equatorial regions. Definitely worth checking out.

Tuesday, September 30, 2008

The Volcanism on Io article on Wikipedia has been going through a peer review for the last couple of weeks. Additional comments for the peer review and edits to improve the article are useful. In particular, the article's lead section is need of expansion to fit the overall length of the article.

Feel free to improve the article, even if it is just for grammar. Let's see if we can't get two Io-related articles to Featured Article status.

Wednesday, September 24, 2008

On Monday, I received my copy of the book Volcanism on Io: A Comparison with Earth by JPL researcher Ashley Davies. This book, by Cambridge University Press, was published late last year. I had considered picking up a copy since it was published, but the cost of the book ($133 on Amazon.com) was a significant barrier. Thankfully due to some lowered expenses this month, I was able to pull the trigger on buying this book.

Volcanism on Io is a review of our current knowledge, post-Galileo, of Io's volcanic activity. This is a much more focused publication compared to the other major post-Galileo Io book, Io After Galileo, edited by Rosaly Lopes and John Spencer with chapters contributed by nearly 30 authors, including yours truly. The book focuses on modeling of volcanic activity, particularly how thermal emission observed from remote instruments can be related to the style of volcanic activity. Davies also spends several chapters on reviewing our current ideas for the eruption styles at several distinct volcanoes, including Loki, Pele, Tvashtar, Prometheus, Amirani, and Pillan.

The meat of the book comes from Davies's explanation of his lava cooling model, presenting step-by-step the various aspects of it including the equations he uses. I wish more diagrams were used to show how some of the variables he uses inter-relate, making some parts of his explanation a bit hard to follow. Also, the chapter in question, Models of Effusive Eruption Processes, is largely a rewrite of the author's 2005 paper on the subject. This fact highlights my most important criticism of this book. Davies does a great job in covering the subjects that are in his wheelhouse: NIMS observations of Io's volcanic activity, internal structure, and modeling of terrestrial and ionian volcanism. Discussion of subjects that are less so, like volcanic plumes and geomorphology, seem to rushed. For example, I would have loved to have seen a chapter covering modeling of volcanic plumes in as much detail as the one on effusive eruption modeling.

Volcanism on Io, with the exception of parts of Chapter 7 where more illustrations could have been very helpful in understanding the equations he was presenting, the book is well illustrated, presenting models based on our current understanding of Ionian volcanism. This is particularly useful in his cutaway views showing the envisioned structure of Io's lithosphere in Chapter 18 and of paterae formation in Chapter 15.

Volcanism on Io provides a focused examination of several of Io's volcanoes. Applying the models Davies presented in the preceding chapters, the author provides in this book a detailed analysis of the eruption styles of specific volcanic centers. I almost wished he expanded his analysis to more volcanoes, like Isum (where several eruptions centered on Io's largest fissure were observed by Galileo), Hi'iaka (a patera with a potentially unique formation process), Kanehekili, and Masubi. It should be noted that the manuscript was likely written sometime in late 2006, before the New Horizons flyby as no results from that encounter are presented.

Ashley Davies's Volcanism on Io is an in-depth look at an important aspect of Ionian science, its volcanic activity. The book provides a review of our current state of knowledge in the subject and focuses on Davies's own models for how the observed thermal emission relate to several important eruption parameters, such as volumetric flow rate, and further, how those relate to eruption style. Davies does an excellent job in explaining how these different eruption styles work. I wish Davies had spent more time on subjects that are not in his wheel house, such as the geomorphology of volcanic terrains and volcanic plumes. Still, I definitely recommend this book for people wanting to better understand the nitty-gritty of perhaps the most important aspect of Io science, the active volcanism on display.

Monday, September 22, 2008

Well I finally pulled the trigger on this book and ordered it on Amazon last week. Volcanism on Io: A Comparison with Earth by Ashley Davies is a comprehensive overview of the current state of knowledge into the volcanism displayed on the surface of Io. An overview of terrestrial volcanism and remote sensing studies is provided as a background to better understand what we see on Io.

The book arrived via UPS this morning and am slowly working my way through the book. I plan on providing a thorough review sometime this week on this impressive tome.

Sunday, September 21, 2008

A fresh eruption at Reunion Island's Piton de la Fournaise volcano today produced a new basaltic lava and a large lava pond and an increase in SO2 concentration within its eight kilometer-wide caldera. Thomas Staudacher, from the volcano observatory on Reunion captured the view at left of the caldera showing this fresh flow. While this eruption seems pretty minor, Piton de la Fournaise (or Le Volcan to the local residents) has recently seen an uptick in activity. According to the AFP, an eruption in April 2007 resulted in the partial collapse of the volcano's caldera and included vigorous fire fountaining that reached upwards of 200 meters into the air.

The last major paper on Io out of the Galileo mission was published in the October 2008 issue of the journal Icarus. "Galileo observations of volcanic plumes on Io," by USGS researcher Paul Geissler and NAU grad student Melissa McMillan, describes the observations acquired of Io's plumes during the entire Galileo mission. The abstract can be found at the link above, but the article itself is available to subscribers (individual or institution) only.

In this paper, the authors searched the Galileo SSI data set for volcanic plumes on Io, then used those images to determine particle sizes, column densities, and plume masses.

In all, the authors found plumes at 13 sites spread out across Io. These include optically bright dust plumes (like the one shown at left), faint dust plumes, and gas plumes, with the latter seen in eclipse observations by Galileo. In some cases, the authors found several of these types at a single volcanic center. For example, on I31 in August 2001, a Prometheus-type dust plume was observed at Thor, which was vigorously erupting at the time. A faint outer halo was also observed in the high phase angle images from that orbit. Pele-type plumes, large, faint plumes generated from gas emitted from lava fountains, went largely unseen by Galileo as SSI had poor sensitivity in the ultraviolet where these types of plumes are best seen. Pele's plume was observed on two occasions, during E4 and G29. Another Pele-type plume was also observed at Grian, resulting in a transient large plume deposit. Several Pele-type deposits were also observed, at Dazhbog and Tvashtar, while additional changes at Pele suggest that additional large plumes existed during the Galileo mission.

The authors then examined the visible-light spectrum of various dust plumes to determine the mean particle size and total plume mass. The authors determined that the small, optically-dense plumes seen at such volcanoes as Zamama, Pillan, and Prometheus consist of course-grained "ash" particles. Combined with the presence of a central dense column in these plumes, and the authors suggest that these particles erupt with the gas in the plume. Typical mass for these plumes was found to be around 106 to 107 kg. The authors also examined the faint outer halo at Thor. They found that the faintness of the plume is not because there is very little dust, but because they are made of much finer particles, 10 nm versus the 80-120 nm found in the brighter core of the plume. With particles that small, the plume would be more easily visible at ultraviolet wavelengths. Strangely enough, the faint outer halo has 10-100 times more mass than the inner, "dense" core. Keep in mind, as well, that even accounting for that inner core, the dust makes up only 10% of mass of these plumes, with the gas making up for the rest of it. The particles in the faint outer halo at Thor (and seen at Loki during the Voyager 1 flyby) are thought to condense directly from the gas in the plume, forming small, sulfur "snowflakes."

The authors also compared the observed plumes to the surface changes found by Galileo. They determined that the surfaces changes were caused by the dense, dust plumes, and not by the fainter gas/snowflake plumes, except in the case of the Pele-type plumes, which produce large, red rings. The deposits made by the gas plumes likely take the form of SO2 frost that is transparent at visible wavelengths. The mass of the plumes suggests that dust fallout makes up only a small fraction of the overall resurfacing on Io.

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I work for the Cassini Imaging team, usually processing Titan and Enceladus images and making maps of Titan based on our images. When I am not working or studying, I'm...I forget. I watch a lot of movies I guess.